Variance in Bidirectional Reflectance over Discontinuous Plant Canopies

An exploratory study of the variance of the bidirectional reflectance over discontinuous plant canopies indicates that the patterns in variance can be related to the properties of the plant canopies. The spatial variance of the bidirectional reflectance calculated from ASAS images shows peak values at the hotspot and near nadir. This behavior can be explained by the geometric effect of discontinuous tree crowns and the regularization effect. Validation of Jupp and Woodcock’s two-component geometric optical (GO) model (1992) shows that it captures the basic features of the spatial variance of the bidirectional reflectance over discontinuous plant canopies. Their two-component GO model is modified to account for the spatial interactions of four scene components. Validation shows that the modified GO model improves predictions. This exploratory study will benefit future use of directional imagery to recover surface parameters by helping characterize the distributional properties of directional imagery.